This invention generally relates to optical correction, and in particular provides methods, devices, and systems for mitigating or treating presbyopia and/or other vision conditions. Exemplary embodiments employ aspherical refractive corrections for providing appropriate accommodative power with changes in pupil size.
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, the effects of ciliary muscle contraction increases the optical power of the lens of the eye to focus at nearer distances. Hence, accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia normally develops as a person ages, and is associated with a natural progressive loss of accommodation, sometimes referred to as “old sight.” The presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. Although the condition progresses over the lifetime of an individual, the effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost most of its elastic properties and has only limited ability to change shape. Residual accommodation refers to the amount of accommodation that remains in the eye. A lower degree of residual accommodation contributes to more severe presbyopia, whereas a higher amount of residual accommodation correlates with less severe presbyopia.
A variety of methods and devices for treatment of presbyopia have been employed, with varying results. The goal of such treatments is generally to allow the eye to see clearly both distant objects and near objects. Reading glasses have traditionally allowed the eye to focus on and maintain a clear image of near objects by adding plus power diopter to the eye, using an approach similar to that applied for treatment of farsightedness or hyperopia. To facilitate viewing both near and far objects, presbyopia has also been treated with bifocal eyeglasses. A variety of other approaches have also been suggested, but none of the known presbyopia-treatment modalities that are commonly used by patients have been shown to be without drawbacks for at least some cases.
In work associated with embodiments of the present invention, it has recently been proposed to provide refractive shapes which take of advantage of changes in a size of a patient's pupil with changes in viewing distances, so as to provide enhanced optical imaging. U.S. patent application Ser. No. 10/738,358 entitled “Presbyopia Correction Using Patient Data,” as filed on Dec. 5, 2003, presents a variety of approaches for establishing prescriptions that mitigate or treat presbyopia of particular patients. Suitable shapes may be optically optimized, scaled or otherwise varied, and/or may provide optical powers that change with pupil size, with the preferred prescriptions often being tailored to measurements of a patient's eye at differing viewing conditions. U.S. patent application Ser. No. 10/892,386, as filed on Jul. 14, 2004, and entitled “Correction of Presbyopia Using Adaptive Optics and Associated Methods” describes systems and devices which may be suited for accurately measuring characteristics of the eye at differing viewing distances. Both these references are incorporated herein by reference. By taking advantage of these recent improvements, many patients may experience enhanced abilities to view at different viewing distances without the inconvenience of reading glasses, bifocals, or the like.
While the recent proposals may represent a significant advancement in the art, as with many such successes, still further improvements would be desirable. In particular, work in connection with embodiments of the present invention indicates that the benefits of pseudo accommodation can be limited in at least some cases. Hence, it would be advantageous to provide improved devices, systems, and methods for treatment of presbyopia, and particularly to provide such improvements so as to extend the benefits of the recently proposed presbyopia mitigation techniques to additional individual patients, groups of patients, and the like. It may also be advantageous to increase the clinical efficacy of presbyopia-mitigating techniques so as to improve optical imaging, acuity, and/or patient satisfaction.